6-60mm HSS Step Cone Drill Bit Hole Cutter Set 12 Steps Metric Step Drill Shank( Dia 13mm) - Compared with ordinary twist drill shaking small, do not need to use the central punch can also open a beautiful aperture out. Do not need to use the center punch, compared with ordinary twist drill is not easy to break site construction, a ladder drill a variety of specifications apply. Unique step structure, a drill can open a variety of size aperture size, a step drill drill arrived on a box. Deburring, chamfering, oval hole expansion, twist drill can not complete the function it becomes possible. The use of tools pistol drill, bench drill while the side of the water cooling when working, can effectively extend the life of the drill, drill speed 250-400 rpm recommended.